1. Field of the Invention
This invention relates to in-line material handling systems for transporting a workpiece from one processing station to another. In particular, the invention is used with systems for transporting metal plate to and from a burning station in which a flame cutting machine is positioned above a water table.
2. Description of the Prior Art
Use of a flame cutting machine generates much pollution in the form of swarf and dross. In order to contain this pollution, the workpiece has been sometimes placed upon closely spaced burning bars positioned above a water table. As the workpiece was cut, the swarf and dross fell into and collected in the water table. The presence of water beneath the workpiece helped to reduce the pollution created and the amount of hot metal present during cutting.
After the flame cutting process was completed, the workpiece was removed from the burning bars by an overhead crane. Although the pollution was substantially reduced by the use of a water table, operation of the flame cutter was not continuous as considerable downtime was needed for removing the finished workpiece, placing another workpiece on the grate and removing swarf and dross from the water table.
More recently, a conveyor system comprising a sprocket chain supporting cutting bars which passes the workpiece beneath the flame cutting machine and over the water table has been substituted for the fixed burning bars so that workpieces can be placed in-line while the flame cutting machine is in operation. After a workpiece is cut, the conveyor system can advance it to an off-loading station where it can be removed and at the same time advance a new workpiece to the burning station. Thus, there is less downtime between cutting operations.
In addition to cutting bars, the sprocket chain of the conveyor system can be designed to support slag collecting elements that catch and remove the swarf and dross from the water table. In order for the slag collecting elements supported on the sprocket chain to function properly and to avoid damaging the slag collecting elements during the burning process, they are submerged below the water level in the water table.
An example of this type of material handling system is the subject of U.S. Patent Application Ser. No. 917,102, filed June 19, 1978, and issued as U.S. Pat. No. 4,220,318. In a system disclosed in that application, an endless sprocket chain conveyor which supports lateral burning bars and slag collector elements, passes through substantially rectangular openings near the top portion of the end walls of a water table located beneath a flame cutting machine. Spaced along the sprocket chain at measured intervals are transition links in the shape of an inverted U which, when the workpiece is positioned beneath the flame cutting machine, are centered over the openings in the end walls of the water table. Thus, the end doors in the water table can be closed and the water level raised to submerge the sprocket chain, slag collecting elements and/or burning bars below the workpiece to protect them during the cutting operation. The transition links allow the end doors to be sealed without engaging or interfering with the sprocket chain since the doors fit within the inner portion of the inverted U.
However, in certain applications there may be disadvantages to this system. The shape of the transition link results in a sprocket chain conveyor having a high profile which requires additional height clearance at each end of the chain conveyor. Another disadvantage of this transition link design is that the link is fabricated from relatively heavy material having sufficient strength to withstand a large bending moment caused by tension on the sprocket chain during use and shock loading resulting from stopping and starting the conveyor. Therefore, a need exists for a water table having an end door adapted to accommodate a sprocket chain conveyor having a low profile transition link.